I get the message "Undefined" when I upload a CSV.
There are known cases when users try to upload a .csv and get a message saying "undefined".
In such cases generate a new .csv and ensure that the file encoding is set as UTF-8. This ensures that special characters used in a variety of languages such as Spanish, German, French and others are encoded in a way which will be imported correctly.
Note: Some Excel-Versions (e.g. Excel for Mac) do not encode in UTF-8 out of the box. It depends on which version and system you are using. If you want to reliably export .csv data for uploads into Datawrapper please search on Google on how a specific version of Excel exports data as a .csv. In cases where UTF-8 export is not available, there is usually a workaround for correct encoding.